1. Field of the Invention
The invention relates to timing-based servo tape formatting. Specifically, the invention relates to apparatus, systems and methods for limiting frame spacing error during timing-based servo pattern fabrication.
2. Description of the Related Art
Timing-based servo systems are commonly implemented to align recording heads during read/write operations. These systems are key to enabling increased data storage density, as they provide precise track-following capabilities across closely spaced tracks. This ability to stay “on track” facilitates the ability of the industry to move to higher and higher track densities.
During the manufacturing process, timing-based servo bands are written to tape by a servo write head and used as a reference to position data tracks. Each servo band includes a pattern of repeating servo frames along a length of the tape. A servo frame includes multiple servo bursts, or groups of servo stripes, where each burst is written at an angle with respect to a consecutive burst.
The servo write head used to write the servo pattern to tape is normally lithographically fabricated to mirror a single servo sub-frame having two opposing servo stripes. The pattern is embossed onto the tape by pulsing the write head a predetermined number of times to create the bursts. For example, a typical servo frame includes an A burst, a B burst, a C burst and a D burst. The A and B bursts normally include five stripes each, while the C and D bursts contain four stripes. Traditionally, therefore, a servo write head pulses five times to simultaneously emboss the A and B bursts, and then pulses four times to emboss the C and D bursts. Spacing between frames and sub-frames is precisely controlled by tape speed and pulse timing.
Some variance in frame spacing is inevitable, however, due mechanical tolerances and fluctuations in tape speed and tension. This variance may be exacerbated where extremely thin magnetic tape is used to maximize the amount of data that can be stored on a reel. Indeed, reduced tape thickness can increase tape sensitivity to variations in speed as the tape is transported from reel to reel.
Recent developments in servo system technology have been directed to reducing an incidence of frame spacing error by modifying the servo write head used to create the servo pattern. One system, for example, teaches simultaneously embossing three servo stripes per frame to create an “N” pattern of servo bursts. This system effectively reduces an opportunity for spacing variances between sub-frames by fixing a distance between B and C bursts, as well as between A and B bursts.
This solution, however, tends to negatively impact system dynamics. Specifically, this solution changes the servo pattern, thereby impeding backward compatibility with traditional tape drives. This solution also affects the update rate of longitudinal position (“LPOS”) information included in the servo pattern.
From the foregoing discussion, it should be apparent that a need exists for a system and method to limit frame spacing error during servo pattern fabrication. Beneficially, such a system and method would minimize spacing error between frames and sub-frames of a servo pattern while maintaining backward compatibility with traditional tape drives. Such a system and method are disclosed and claimed herein.